Short wave transmitter



Patented June 9, 1942 l UNITED STATS SHORT WAVE TRANSMITTER ApplicationMarch 22, 1939, Serial No. 263,367

2 Claims.

My invention relates to high frequency transmission systems and moreparticularly to radio frequency transmission circuits adapted to supplyenergy to two or more symmetrical loads from an unsymmetrical source ofsupply or from a single symmetrical two conductor line or loop.

It is often desirable to transmit energy from an unsymmetrical sourcesuch as an oscillator or frequency multiplier grounded on one side, totwo or more symmetrical loads, for example, radiating antennae. Thistype of arrangement is particularly useful for supplying energy totransmitting antennae which may be used for defining a beacon course,since under these circumstances it is desirable that the load beproperly balanced in order that the system be efiicient and a suitableradiation pattern be secured. Furthermore, in beacon systems it is oftendesired to separately adjust the power fed to each of the radiatingantennae, so that the course line may be properly defined andmaintained. Similarly it may be desired to connect two or more balancedlines over which energy is transmitted to a single unbalanced line or toa single belanced line.

It is an object of my invention to provide a radio frequencytransmission system which is suitable for intercoupling two or morebalanced lines and an unbalanced line.

It is a further object of my invention to provide a radio transmitter inwhich energy from an unbalanced source is applied to a plurality ofantennae each connected to a separate balanced line.

It is a further object of my invention to provide in a radio transmittera system which permits the independent adjustment of energy to theseparate balanced antennae.

It is a still further object of my invention to provide the combinationof a radio frequency source, a balanced amplifier and a plurality ofbalanced loads connected to the output of the amplifier.

It is a still further object of my invention to provide a radiotransmitter with a balanced line feed for two or more separate antennae,in which the energy fed to the antennae may be separately modulated orkeyed.

It is a still further object of my invention to provide a novel keyingarrangement for use with a pair of symmetrical radio beacon antennae.

The above mentioned and further features and objects of my invention andthe manner of attaining them will be apparent from a particulardescription of my invention made in accordance with the accompanyingdrawing, in which:

Fig. 1 illustrates a preferred embodiment of a radio transmitter made inaccordance with my invention,

Fig. 2 illustrates a form of split stator condenser suitable for use inthe modulation system of Fig. 1, and

Fig. 3 illustrates an alternative modulation sys tern in accordance withmy invention which may be used in place of that disclosed in Fig. 1.

Turning now to the drawing and particularly to Fig. 1, I06 represents asource of radio frequency energy which may be, for example, anoscillator or a frequency multiplier. In source I00 at 1222 is indicateda vacuum tube which may represent the last stage of the radio frequencycircuit within Hill. The anode of tube I02 is connected to a positivevoltage supply as indicated, and is connected through the primary oftransformer I03 to ground for radio frequencies through the radiofrequency condenser Iill. Transformer W3 is designed for highfrequencies and constitutes a single turn for the primary and secondaryso that the coupling between the primary and secondary is made by meansof a distributed inductance and capacity only. Coupling transformer N33is made adjustable so that the coupling between the windings may bevaried.

The secondary of the transformer I03 is connected to ground on one sideand on the other side to a transmission line I04, through a variablepower controlling condenser I05. It is evident that this arrangementforms an unsymmetrical line portion. This unsymmetrical line isconnected to a push-pull amplifier comprising vacuum tubes I06, I01.Since, in order for the vacuum tubes to operate properly in push-pullthe input thereto should :be balanced, I provide a network to achievethis balance indicated generally at I08. At lower radio frequenciesbalanced input may be obtained by merely grounding the center point of atransformer and connecting the outer ends through lines to the grid.However, at higher frequencies balance cannot be obtained so simply. Abalance may be obtained by connecting in series across the line a pairof impedances such as III], III, and connecting these impedances toground through a third impedance I [2. In the circuit shown in Fig. 1,impedances Hi! and HI are inductances, whereas impedance H2 is acondenser. A balance may be obtained in this way provided impedances II6, and III are properly related to impedance H2 in value and are of asign opposite to that of H2.

In the preferred arrangement impedances II I] and III are made equal andimpedance IE2 is made equal to one-half the value of either of theimpedances H0, or III. However, a considerable departure from thisrelationship may ocour in practice, and approximate equality ofimpedances III) and III being suificient, and a considerable variationin the relationship of the impedance values of H2 and III], III beingpermissible for most applications. In order that a complete balance maybe obtained inductances I I U and I I I are arranged so as to have verylittle, if any, mutual coupling between them. A blocking condenser I I3is provided between inductance III and the junction points of III] and'2, so that power may be supplied to the grid of tubes I06 and I!through the leads, IM' independently of each other. This arrangementpermits the use of separate grid meters to indicate the .operation ofthe tubes. The output circuit of the vacuum tubes I06, I01, is connectedto a high frequency variable transformer H5, the primary of which isconnected to a power supply through radio frequency choke H6. Tuningcondensers II! are provided to tune the output of push-pull amplifier.Coupled to the secondary of transformer IE are conductors II 8, H9,which together form a balanced output line. The separate conductors H8,H9, are unbalanced with respect to ground so that each conductor may beconsidered as a further unsymmetrical line. The midpoint of thesecondary of transformer H5 is grounded so that in effect each of linesH8 and I I9 may be considered asan independent unbalanced line with aground return. In lines H8, H9, are provided variable condensers I20,I2I which may serve to independently control the power output over therespective lines.

In line H8 is provided another high frequency network which serves toproduce a balanced output from the unsymmetrical line IIB. This net-Work comprises inductance elements I22, I24, connected similar toinductance elements III], and I I I, and to a variable condenser unitI26, corresponding to condenser H2. Condenser I26 is made variable sothat its impedance may be adjusted to balance precisely transmissionline I26. Similarly, line II 9 is branched to form a balancedtransmission line I29 through a network comprising inductance elementsI23, and I25, and a variable capacity element I27.

To the outer end of transmission line I28 is coupled an antenna I30,shown as a dipole antenna, and to line I29 is coupled another dipoleantenna I3I. While I have shown antennae I39 and ISL as dipoles, itshould be distinctly understood that they may be of any desired form solong as they are designed to form a balanced load. Furthermore, it isclear that instead of leading to antennae, transmission lines I28 andI29 may lead to any desired type of symmetrical load.

If it is desired to use antennae I36 and I3I as a radio beacon, theseantennae should be arranged at a suitable angle with respect to eachother to produce the desired wave pattern. Arrangements of antennae forradio beacon transmission are well known so no specific illustrationthereof is made in this application.

In order that the signals from the separate antennae may bedistinguished, I provide means to modulate the energy fed to theantennae to form the distinctive signals. Any desired modulating meansmay be used as the method of modulation in such as to preserve thesymmetry of the system. In the arrangement according to Fig. 1, Iprovide, for modulating the antennae, a filter, comprising resonantquarter wavelength frames I32 and I33 constituting sections oftransmission line and loosely coupled to the transmission line. Theseframes are coupled to the transmission line inductively primarilythrough capacitive induction and may be precisely tuned by means oftrimming condensers I34, I35. When these frames are properly positionedwith respect to the transmission line and accurately tuned, they willoperate to substantially stop all of the energy from flowing along thetransmission line. Although I have illustrated these tuned coupledsections as open-ended frames, they may have other forms, such as closedframes of proper length or may be of various other formations. Forstructural details of the various forms of transmission modifyingnetworks, reference may be had to Patent No. 2,159,648, issued May 23,1939 on an application of Andrew Alford, Ser. No. 162,853 filedSeptember 8, 1937. Since the filtering action of coupled transmissionline sections, such as shown at I32 and I33 are very critical withtuning, their effect on the flow of energy through transmission linesI28, I29, may be modified byslightly detuning the section. This fact ismade use of in producing the modulation of the energy transmitted to theantennae. Across each of networks I32, I33, I provide split-statorcondensers I36, I31. These condensers are arranged with the fixed platescoupled to the separate conductors of the transmission line, while therotary plates are driven at a uniform rate by means of a motor M9 orother means. Condensers I36 and I3! maye be made with a different numberof notches in the stator plate so that the energy fiowing alongtransmission lines I28, I29 is interrupted at a different rate toimpress a different modulation upon the energy radiated from antennaeI30, I3I.

One form of split-stator condenser suitable for use in the system ofFigure l, is illustrated in Figure 2. This condenser comprises fixedtoothed stators 20I, 262, connected to the opposite side .of a balancedline 290, and a single rotary plate e1ement263. When 263 is rotated at auniform rate the tuning of the condenser is varied periodically,depending upon the speed of the rotor 263 and the number of teeth onstator plates 2DI, 292. Thus a chopping or keying of energy may beaccomplished by means of this rotary .condenser connected across a tunedframe such as I32. The frequency of modulation may be varied by varyingthe number of teeth on the condenser or by driving the rotors of thecondensers at different speeds. The percentage or depth of modulationmay be controlled by so choosing the condensers as to providethe desiredpreciseness of tuning of the coupled sections.

WhileinFig. 1 I have illustrated the arrangement wherein an amplifier isutilized between the source of radio frequency oscillation and the load,it should be distinctly understood that this amplifier may be omitted,and the energy and amplification taken care of in other parts of thecircuit, if desired. Also, it should be understood that the balancingnetwork need not .be composed of two inductances and a single capacityas shown, but may be of any form of impedance so long as they satisfythe requirement specified above. It is thus clear that in placeofinductances IIIIand III of I08,.equal capacities should be substitutedtherefor and an my invention. It should further be understood,

according to the general reciprocity theorem,

7 that instead of a transmitter, the system may constitute a receivingarrangement. Antennae I30, l3! receive radio signals and transmit themover balanced lines to an unbalanced receiver. In Fig. 3, I haveillustrated an alternative form of modulating system which may besubstituted for that illustrated in Fig. 1. In this arrangement 320,32l, 3! and 319, represent the power '1 adjusting condensers and theconductors of the transmission line similar to that disclosed in.Fig. 1. ductances 322, 324 and capacity 326, and in- Similarly thenetwork comprises inductances 323, 325, capacity 326, correspond tosimilar elements in Fig. 1. Loads 330, 33l, may

,, be antennae corresponding to I30, |3l or any other form ofsymmetrical load. The modulating system, however, differs from thatshown in Fig. 1. At 341, 342 are illustrated two halfwave length shortcircuited frames connected at the proper point across balancedtransmission lines 328, 329, respectively. At a point midway of thelength of transmission line sections 34I, 342 are provided shortcircuiting switches 343, 344, which are driven by means of a motor 340.Adjustable short circuiting bars 345, 346 are provided on each of thesections 34l, 342.

This modulating system operates as follows: When a short circuitingswitch 343 is crosswise so as to short circuit the network 3 thisnetwork forms a short circuited quarter wavelength line connected acrosstransmission line 328. Aside from resistance and radiation losses thecircuit will not drain nor hamper flow of energy along transmission lineto load 330. When switch 343 is turned to the open position theeffective circuit from the transmission line extends out to theshort-circuited end of the halfwavelength section 341. This thenconstitutes a half-wavelength short circuited filter across the mainline preventing substantially all of the energy from flowing to theantenna. Thus I the modulation may be obtained by interrupting the flowof energy along the line by means of the short circuiting switch 343.Similarly modulations may be efieoted in the energy of line 329 by shortcircuiting switch 344. These switches may be provided with a pluralityof segments so as to interrupt the flow at difierent rates in the twodifferent lines so as to provide different modulations of the energy forthe two loads. If it is desired to utilize less than 100% modulation,short circuiting bars 345, 346 may be changed in position so as to alterthe length of the section from that of a full half-wavelength.

While I have described my invention with ref erence to figuresillustrating a preferred embodiment thereof, it should be understoodthat this description is merely by way of illustration and not alimitation of the scope of my invention, which is defined in theaccompanying claims.

What I claim is:

1. In a radio beacon transmitter comprising a source of radio frequencyenergy, two balanced antennae, two independent balanced twoconductorlines coupled with said source, and means coupling one of said antennaeto each of said last named balanced two-conductor lines, modulatingmeans connected to each of said twoconductor balanced lines, saidmodulating means comprising a variable impedance network coupled acrosseach of said balanced transmission lines, said network normally ofieringsubstantially no impedance to the passage of said radio frequency energyupon variation of said impedance, said impedance networks eachcomprising a section of transmission line spaced from each of saidbalanced transmission lines and normally detuned with respect to thefrequency to be transmitted and tuning means comprising a variabletuning arrangement operatively associated with said transmission linesection for alternately tuning said sections to said frequency.

2. In a radio beacon transmitter comprising a source of radio frequencyenergy, two balanced antennae, two independent balanced two-conductorlines coupled with said source, and means coupling one of said antennaeto each of said last named balanced two-conductor lines, modulatingmeans connected to each of said two conductor balanced lines, saidmodulating means comprising a variable impedance network coupled acrosseach of said balanced transmission lines, said network normally offeringsubstantially no impedance to the passage of said radio frequency energyalong said transmission lines and ofiering higher impedance to saidenergy upon variation of said impedance, said impedance networks eachcomprising a section of transmission line spaced from each of saidtwoconductor lines and coupled thereto, the degree of coupling betweensaid sections and said two conductor lines being difierent at one partthan at another, said sections being normally detuned with respect tosaid frequency, and means for modulating said energy in saidtransmission lines, comprising means for periodically tuning saidsection substantially to said particular irequency whereby energy willperiodically be prevented from flowing in the part of said line pastsaid section.

PAUL F. BYRNE.

